1. Field of the Invention
The invention relates to an arrangement of optical fibers. The invention further relates to a method of forming an optical fiber array. Finally, the invention relates to a modulation device and a lithographic apparatus comprising such arrangement.
2. Description of the Related Art
Charged particle multi-beamlet systems are known in the art, for example from U.S. Pat. No. 6,958,804 and/or from WO2009/127659, both in the name of the applicant, the latter one, being specifically adapted for very high volume throughput operation. Such lithography system uses a plurality of charged particle beamlets to transfer a pattern to a target surface. The system may operate with a continuous radiation source or with a source operating at constant frequency. Pattern data are sent by means of pattern data carrying light beams to a modulation device. The modulation device may then include light sensitive elements capable of converting received light signals into corresponding electric signals. The electric signals are then used to modulate the beamlets by electrostatic deflection. Finally, the modulated beamlets are transferred to the target surface.
Modulated light beams may be transferred using optical fibers. However, in order to obtain accurate data transfer, such optical fibers need to be aligned very accurately with respect to the light sensitive elements to allow accurate and reliable data transfer. In multi-beam charged particle lithography systems as described above the number of optical fibers is extremely high, and may easily be in the order of 10,000. Consequently, positioning of the fibers needs to be done very accurately. Such accurate placement is not straightforward. Furthermore, the volume being occupied by such large amount of optical fibers is preferably as small as possible, to enable the apparatus to be of limited size. Therefore, it is an object of the invention to provide an optical fiber arrangement or fiber array with very accurate positioning of the fibers, while occupying limited space.